Liquid-cooled multi-disc brake

ABSTRACT

The invention concerns a liquid-cooled multi-disc brake (29) as used in transmission systems. The object of the invention is to improve the cooling of a multi-disc brake (29) exposed to high stresses owing to frequent use. In order to increase the throughput of coolant through the multi-disc brake (29) and to intensity the coolant circulation, one inner disc carrier (10) of the multi-disc brake (29) is designed as feeder wheel (48). Such a characterized multi-disc brake (29) is preferably used within the transmission system for heavy construction vehicles such as wheeled loaders, since liquid-cooled multi-disc brakes (29) in these utility vehicles are frequently used at full engine power. However, the use of the multi-disc brake (29) according to the invention is not limited to this particular application.

The invention concerns a liquid-cooled multi-disc brake in which aninner disc carrier is fixedly supported on a drive shaft for supportinginner brake discs, and outer brake discs, which are supported on anouter disc carrier, a feed pipe for coolant leading to the inner disccarrier, in which coolant flows through radially extending ducts of theinner disc carrier toward the inner and outer brake discs and dischargesvia an outlet of the outer disc carrier.

Liquid-cooled multi-disc brakes of the above mentioned kind are oftenused in transmission systems. Such multi-disc brakes are preferred, inparticular, in heavy utility vehicles, such as wheeled loaders. Thoseutility vehicles are known to be subject to extreme conditions of use.The liquid-cooled multi-disc brakes are accordingly also exposed to highstresses. It is not uncommon that in a wheeled loader, for instance, inthe industrial performance "load" that the multi-disc brakes can beactuated up to seven times per minute at full engine power. Under such astress it is no wonder that the coolant can reach high limittemperatures, as will particularly occur in case of insufficient coolantthroughput and high external temperatures.

DE-OS 37 32 760 has disclosed a friction brake with liquid cooling inwhich the coolant is fed to an annular space after which it is splashedout between the discs of a multi-disc brake making use of thecentrifugal force. The circulation of the coolant is dependent on theactuation of a multi-disc brake, since during the closing or opening ofthe multi-disc brake the feed pipe is either opened or closed. This isdisadvantageous, since the temperature of the multi-disc brake increaseswith the delay per time unit. Additionally, the coolant throughputthrough the disc assembly of that multi-disc brake is too slow. Thevolume of coolant available is insufficient and accordingly becomesquickly heated to high temperatures under unfavorable conditions.

European patent 00 76 387 B1 has disclosed a vehicle axle having acoolant circuit wherein a pump takes care of the forced circulation ofthe coolant. The coolant is sucked by a pump from a collector via asuction tube and fed via additional pipelines to the disc assembly ofthe multi-disc brake. The pump is a relatively expensive, importantcomponent which must be protected with special care against foreignbodies. In the solution known already, this was done by inserting afilter which was to keep away from the pump the portion, known to berelatively large, of foreign bodies in the circulating coolant. Toensure a reliable operation, a control of the filter is needed, whichmeans an elevated maintenance cost.

British patent 20 91 350 A has also disclosed a wheel head for sprocketwheels of vehicles where the hub, in which a planetary transmission andmulti-disc brake are accommodated, is partially filled with coolant. Thehub is rotatably mounted on a hollow axle and is penetrated by a driveshaft. Between the drive shaft and the hollow axle an annular gap isformed through which the coolant flows toward the wheel head. Theannular gap discharges in a transversal hole in the drive shaft. A holeextending in the longitudinal direction of the drive shaft createscommunication between the transversal hole and radially extending ductsin the drive shaft and a disc carrier, which is part of the internalcentral gear of the planetary transmission. The coolant exiting on theperiphery of the multi-disc brake is drained via openings in a ring-gearcarrier of the planetary transmission. In this arrangement, theconstruction of the feed pipe for the coolant is, on one hand, expensivefrom the point of view of manufacturing and, on the other hand,disadvantageous in relation to the strength of the drive shaft. Theremust further be used an external pump--having the above mentioneddisadvantages--in order to circulate the coolant.

The problem to be solved by this invention is to improve a liquid-cooledmulti-disc brake of the kind mentioned above by increasing the coolantthroughput as well as the intensity of the coolant circulation. Inaddition, the disclosed arrangement must be insensitive to the action offoreign bodies.

The problem on which the invention is based is solved by designing theinner disc carrier as a feeder wheel which rotates at the speed of thedrive shaft and against which coolant flows in the region of the driveshaft--relative to the longitudinal extension thereof. The design of thedisc carrier as a feeder wheel, which rotates at the speed of the driveshaft, produces a considerable increase of the coolant throughput perunit of time. Due to the inner brake discs that rotate at the speed ofthe drive shaft, the high specific braking performance of the multi-discbrake is preserved. The design of the disc carrier as a feeder wheelalso permits a simple construction at a reasonable cost. The feederwheel can be simply constructionally constituted so that the arrangementis fully insensitive to foreign bodies carried in the coolant. The disccarrier is disposed in a manner such that the coolant flows axiallyagainst the feeder wheel in the region of the drive shaft. Such feedingof the coolant has a great advantage in that the cross section of thedrive shaft is fully preserved, that is, it is not diminished.

In the passage region of coolant into the feeder wheel, the disc carrierhas an inlet gap substantially congruent with the annular gap, in whichthe inlet gap lies opposite to the annular gap and at a small axialdistance relative to a longitudinal central plane of the drive shaft.Said small distance produces a safe guidance of the coolant and preventsturbulences in the passage region (features and advantages of claim 2).

According to another advantageous feature of the invention, the inletgap forms the beginning of an annular feed gap of the feeder wheel which--relative to the longitudinal extension of the drive shaft--has asubstantially axially oriented section which converts into a radiallyoriented section which on its external end is limited by a collar of thedisc carrier, the radially extending ducts penetrating the collar (claim3). In terms of fluid mechanics, the construction of the feeder wheelensures a favorable deviation of the coolant from the discharge area ofthe annular gap to the collar of the disc carrier from where it entersin the brake discs of the multi-disc brake.

The coolant throughput can be controlled by the arrangement andconstruction of the feed elements in the feed gap. The feed elementspreferably extend--radially --as seen in the topview on the feederwheel. The radially oriented feed elements ensure a reliable conveyanceof the coolant in both directions of rotation of the disc carrier (claim4).

A favorable solution from the point of view of the finishing techniqueconsists in that the disc carrier is composed of two partsinterconnected in a manner such that --relative to the longitudinalextension of the drive shaft--the axial distance from each other isdetermined by spacers which establish the inner width of the radiallyoriented section of the feed gap (claim 5). The arrangement becomesspecially simple if the feed elements are also designed as spaces (claim6) having bolt holes in which fixing bolts can be screwed (claim 7).Both parts of the disc carrier can be screwed together in a simplemanner. It is also possible to use a rivet instead of a screwconnection.

According to another feature of the invention, a simple solution fromthe point of view of the finishing technique consists in that one partof the disc carrier is a ring which is centered by its external diameterin a recess on the collar of the disc carrier and whose internaldiameter is identical with the external diameter of the inlet gap (claim8).

A further simplification can be obtained by connecting the feed elementswith the ring to form a combined part (claim 9).

According to another feature of the invention, the disc carrier has onthe side opposite the inlet gap passage openings, which in relation tothe longitudinal extension of the drive shaft extend substantiallyaxially oriented (claim 10). During forward or reverse travel the disccarrier rotates at the speed of the drive shaft so that no coolant isnormally fed or discharged through the passage openings. It is only whenthe disc carrier stops, that the passage openings effect a bypass withthe inlet gap of the pump impeller or the directly axially oppositeannular gap. The coolant can speedily flow off via the connectiondescribed, whereby a quick removal of heat is ensured.

The steps proposed in sub-claims 11 and 12 additionally serve to promotethe quick discharge of coolant.

The steps proposed in sub-claims 13, 14 and 15--either separately orcombined--serve the purpose of advancing the throughput of the coolantthrough the inner and outer brake discs of the multi-disc brake. Theproposed construction of the inner and outer brake discs results inadditionally supporting the action of the feeder impeller. The fact thatthe coolant is advanced in both directions of rotation of the disccarrier is of special advantage here.

When using the multi-disc brake in a wheel head whose ring-gear carrierpositively meshes with an external gearing in an internal gearing of thering gear, it is specially advantageous, in order to promote thedischarge of the coolant, that the external gearing of the ring-gearcarrier has passages for the coolant extending in a longitudinaldirection and distributed on the periphery of the ring-gear carrier(claim 16).

According to another feature of the invention, it is advantageous, toproduce an effective discharge of the coolant, that the passagesdischarge in a collector ring connected with the drain pipe for thecoolant (claim 17).

The feature proposed in sub-claims 19, 20 and 21 concern the feeding ofthe coolant to the feeder wheel. From the point of view of fluidmechanics it is advantageous cup-like to enlarge the external walls ofthe annular gap in a direction toward the disc carrier (claim 19).

The coolant can be fed exclusively via the annular gap (claim 20).

It is further possible to feed the coolant via a feed pipe passedthrough the hollow axle, extending parallel to the drive shaft anddischarging in the annular gap (claim 21). Let it be mentioned in thisconnection that the feed pipe preferably discharges in the region of thecup-like enlargement of the external walls of the annular gap.

In an advantageous embodiment of the invention, a quick removal of heatis obtained by discharging the coolant from a wheel head, (when thedrive shaft is stationary), outwardly via the drain pipe passed throughthe ring-gear carrier via the passage openings of the disc carrier, theinlet gap of the feed gap and the annular gap (claim 22).

Another structural simplification of the arrangement can be obtained inanother embodiment of the invention in that instead of the drain pipeleading through the ringgear carrier, the coolant is discharged from thehead wheel, when the drive shaft is stationary, via passage openings ofthe disc carrier, the inlet gap of the feed gap and the annular gap(claim 23).

The volume of coolant can be additionally increased in that the drainpipe and/or the annular gap communicate(s) with the interior of an axlebody. In this case the axle body simultaneously serves as heat exchangerfor cooling the coolant.

Other essential features and advantages derived therefrom result fromthe explanation that follows of several embodiments of the inventionwith reference to drawings. In the drawings:

FIG. 1 shows a section extending in the longitudinal direction of adrive shaft through a wheel head according to the of the invention;

FIG. 2 is a section through a disc carrier;

FIG. 3 shows a possible construction of one part of a disc carrier;

FIG. 4 is a section through a wheel head according to another of theinvention; and

FIG. 5 shows the structurally further simplified wheel head of FIG. 4.

The wheel head 1, shown in section, is a component part of a vehicleaxle (not shown), for instance, for a heavy wheeled loader. A hollowaxle 2 is firmly screwed to an axle body (which is also not shown). Theexternal end of hollow axle 2 carries a ring-gear carrier 3. Ring-gearcarrier 3 is fixedly connected with the hollow axle 2 via an engaginggearing 4 and is axially secured by a locknut 5.

A coaxial bore 6 of the hollow axle 2 is penetrated by a drive shaft 7.The drive shaft 7 is operatively connected with an axle bevel gear (notshown) of a differential transmission. An annular gap 8 is formedbetween the drive shaft 7 and the bore 6 of the hollow axle 2.

The external wall of the annular gap 8 (which is identical to thesurface of bore 6) is provided with a cup-like enlargement 9 on anexternal end.

For ease of assembly, the drive shaft 7 is divided in the region of aninner disc carrier 10. The external section 11 of the drive shaft 7 isdesigned in one piece with a sun 12 of a planetary transmission 13. Thedrive shaft 7 is fixedly connected to the external section 11. The fixedconnection results by way of similarly designed engaging gears 38.

The ring-gear carrier 3 is provided with another engaging gearing 14 onits external periphery. A ring gear 15 of the planetary transmission 13rests via said engaging gearing 14 on the ring-gear carrier 3. The ringgear 15 is provided with an internal gearing 16. Several planetary gears17, of which only one is shown, mesh by their external gearing 18 in theinternal gearing 16 of the ring 15, and thus rest on ring gear 15. Theplanetary gears 17 are further driven by the sun 12.

The planetary gears 17 are rotatably mounted on a web 19 whichsimultaneously assumes the function of a cover. The web 19 is fixedlyconnected with a hub 20. The hub 20 is rotatably supported via wheelbearings 21 and 22 on the hollow axle 2, or on the ring-gear carrier 3,fixedly connected therewith. The interior of the hub 20 is outwardlysealed by means of a seal ring 23.

The disc carrier 10 has an annular flange 24 on the side facing theplanetary transmission 13, which on its external periphery converts to acollar 25 which faces the ring-gear carrier 3, and extends in a parallelorientation with drive shaft 7. The collar 25 has an external gearing 26upon which inner brake discs 27 are lined up in a known manner. Togetherwith outer brake discs 28, which are supported on the internal gearing16 of ring gear 15, a multi-disc brake 29 is formed. The ring gear 15forms an inner disc carrier. The multi-disc brake 29 is hydraulicallyactuatable. For this purpose, an annular piston 30 is provided by whichthe multi-disc brake 29 can be actuated in the closing direction bymeans of a pressurized medium which is passed into a (partly shown)pressurized-medium pipe 31. If the pressurized-medium pipe 31 ispressureless, recoil springs, (not shown) reset the annular piston 30.In addition the inner and outer brake discs 27 and 28 of multi-discbrake 29 rest axially on an end shim 32 which is retained inside thering gear 15 by means of a guard ring 33.

From FIG. 2 the further construction and the installation position ofdisc carrier 10 in relation to annular gap 8 can be deduced. The collar25 of the disc carrier is provided with radially extending ducts 34. Theducts 34 are situated to discharge between two adjacent inner brakediscs, that is, the ducts are oriented with respect to an outer disc 28.

The disc carrier 10 is completed by a ring 35 centered by its externaldiameter in a recess 36 of the collar 25. Disc carrier 10 is thereforecomposed of two parts. The disc carrier 10 sinks by a hub 37 into thecup-like enlargement 9 of the annular gap 8. An inlet gap 40 liesopposite to the annular gap 8--maintaining a small axial distance 39,relative to the longitudinal extension of drive shaft 7. Both theannular gap 8 and the inlet gap 40 are preferably congruent in order toprevent turbulences in the transition zone between the annular gap 8 andthe inlet gap 40. The inlet gap 40 constitutes the beginning of anannular feed gap 41. The feed gap 41 has--relative to the longitudinalextension of drive shaft 7--a substantially axially oriented section 42that converts into a radially oriented section 43. The latter is limitedon its external end by the collar 25 of the disc carrier 10. Feedelements 44 are situated in feed gap 41. In the instant case, the formerare three radially oriented webs which are part of the ring 35, and areoffset with respect to each other by 120° (seen in longitudinaldirection of drive shaft 7). The feed elements 44 situated in the feedgap 41 further assume the function of spacers which determine theinternal width of radially oriented section 43 of the feed gap 41. Thefeed elements 44 are further provided with bolt holes 45 shown as dottedlines in FIG. 2. Fixing bolts 46 are screwable in the bolt holes 45. Theparts of the disc carrier 10 could also be interconnected by rivets asopposed to the screw connections.

FIG. 3 diagrammatically reproduces another possibility of theconstruction of the ring 35 of the disc carrier 10. The illustrationshows the ring 35 in a topview. Said ring 35 forms, when inserted, abucket wheel. The ring 35 has for this purpose a multiplicity ofradially oriented feed elements 44. Two diametrically opposite boltholes 45 are present in order to be able to connect the ring 35 with thedisc carrier 10.

The disc carrier 10 has on the side opposite to the inlet gap 10,passage openings 47 which, relative to the longitudinal extension ofdrive shaft 7, extend obliquely and inclined in a direction to the inletgap 40 forming an acute angle.

The friction surfaces of the inner and outer brake discs 27 or 28 areprovided with depressions (not shown) which form passages for thecoolant. They extend either radially or curved, as seen in a topview, onthe friction surfaces so that in both directions of rotation ofmulti-disc brake 29, a feeding action is exerted on the coolant.

It can be understood from the explained construction of the disc carrier10 that it is designed as a feeder wheel 48. The latter revolves at thespeed of drive shaft 7 and the coolant flows axially against it. Thisoccurs in the region of the annular gap 8, in the case of passage intothe inlet gap 40.

In the embodiments of FIGS. 1 and 2 coolant delivered by feeder wheel 48is collected in a collector ring 49 after passing of the inner and outerbrake discs 27 or 28. Passages 50 in the external gearing of thering-gear carrier 3 facilitate the discharge of the coolant into thecollector ring 49. From the collector ring 49, at least one drain pipe51 leads through the ring-gear carrier 3 to another drain pipe 52 whichextends parallel to drive the shaft 7.

In the embodiment of FIG. 1, the annular gap forms the feed pipe (arrow53) for the coolant which runs into feeder wheel 48 from the interior ofthe axle bridges The coolant is drained via the collector ring 49 andeither drain pipe 51 or 52. In the construction of FIG. 4, the coolantis fed (arrow 53) through a separate bore 54 into the hollow axle 2,which discharges in the region of the cup-like enlargement 9 in theannular gap 8. The coolant is drained via two separate trains of pipes.Together with the discharge of the coolant via collector ring 49 anddrain pipe 51 or 52, an additional possibility of drainage for thecoolant is offered through axially the oriented passage openings 47 ofthe disc carrier 10. When the disc carrier 10 is stationary, ashort-circuited connection is formed between passage the opening 47 andthe inlet gap 40 of the feeder wheel 48. The coolant is additionallydrained via the annular gap 8, as indicated by arrow 55.

In the embodiment of FIG. 4 the coolant is discharged exclusively viathe passage openings 47, the inlet gap 40 and the annular gap 8. In thissolution, the collector ring 49 and drain pipe 51 or 52 are eliminated.

All solutions stand out by the construction of disc carrier 10 as afeeder wheel 48. The coolant flows axially through the feeder wheel 48.The feeder wheel 48, which revolves at the speed of drive shaft 7,effects an intensive delivery of the coolant. The delivery of thecoolant is also maintained in the marginal zones of the inner and outerbrake discs 27 and 28, since they also exert a feeding action upon thecoolant.

The design of disc carrier 10 as a feeder wheel 48 has as a consequence,that together with an elevated throughput of the coolant, that wheel hub20 almost completely fills with coolant. For cooling the multi-discbrake, a large volume of coolant is available. It is also advantageousthat the feeder wheel 48 delivers coolant in both directions of rotationof disc carrier 10. A quick removal of heat from the wheel head isspecially ensured when the coolant--as explained above--is dischargedvia two separate trains of pipes.

Reference numerals

1. wheel head

2. hollow axle

3. ring-gear carrier

4. engaging gears

5. locknut

6. bore

7. drive shaft

8. annular gap

9. enlargement

10. inner disc carrier

11. section

12. sun

13. planetary transmission

14. engaging gears

15. outer disc carrier, ring gear

16. internal gearing

17. planetary gears

18. external gearing

19. web

20. wheel hub

21. wheel bearing

22. wheel bearing

23. seal ring

24. annular flange

25. collar

26. external gearing

27. inner brake discs

28. outer brake discs

29. multi-disc brake

30. annular piston

31. pressurized-medium pipe

32. end shim

33. guard ring

34. ducts

35. ring

36. recess

37. hub

38. engaging gears

39. axial distance

40. inlet gap

41. feed gap

42. axially oriented section

43. radially oriented section

44. feed elements

45. bolt holes

46. fixing bolts

47. passage openings

48. feeder wheel

49. collector ring

50. passages

51. drain pipe

52. drain pipe

53. feed pipe

54. bore

55. drain pipe

What is claimed is:
 1. A liquid-cooled multi-disc brake (29) in which isfixedly supported upon a drive shaft (7), an inner disc carrier (10) forsupporting inner brake discs (27) and outer brake discs (28) which aresupported on outer disc carrier (15), a feed pipe (53) for coolant whichleads to said inner disc carrier designed as feeder wheel (48), saidcoolant flowing through radially extending ducts (34) of said inner disccarrier (10) toward said inner and outer brake discs (27, 28 anddischarging, via a drain pipe (51, 52) of said outer disc carrier (15),characterized in that said feed pipe (53) is designed as annular gap (8)and said disc carrier (10) has an inlet gap (40) designed substantiallyidentical with said annular gap (8) and which--relative to alongitudinal central plane of said drive shaft--is opposite to saidannular gap (8) at a short distance so that the coolant flows axiallyagainst said feeder wheel (48) in the region of said drive shaft(7)--relative to a longitudinal extension thereof.
 2. A multi-disc brakeaccording to claim 1, characterized in that said inlet gap (40) formsthe beginning of an annular feed gap (41) of said feeder wheel (48),which in relation to a longitudinal extension of said drive shaft has asubstantially axially oriented section (42) which converts into aradially oriented section (43) which on its external end is limited by acollar (25) of said disc carrier (10), said radially extending ducts(34) penetrating said collar (25).
 3. A multi-disc brake according toclaim 1 characterized in that feed elements (44) which extend in aradial orientation are situated in said feed gap (41).
 4. A multi-discbrake according to claim 1, characterized in that said disc carrier (10)is composed of two parts (10, 24, 25 and 35) interconnected in a mannersuch that their axial distance from each other--in relation to thelongitudinal extension of said drive shaft --is established by spacerswhich determine the internal width of said radially oriented section(43) of said feed gap (41).
 5. A multi-disc brake according to claim 1,characterized in that said feed elements (44) are designed as spacers.6. A multi-disc brake according to claim 3, characterized in that saidfeed element s(44) have bolt holes (45) in which fixing bolts (46) canbe screwed.
 7. A multi-disc brake according to claim 3, characterized inthat one component part of said disc carrier (10) is a ring (35) whichis centered by its external diameter in a recess (36) on said collar(25) of said disc carrier (10) and whose internal diameter is identicalwith the external diameter of said inlet gap (40).
 8. A multi-disc brakeaccording to claim 3, characterized that in said feed elements (44) forma combined part with said ring (35).
 9. A multi-disc brake according toclaim 1, characterized in that said disc carrier (10) has passageopenings (47), on the side opposite said inlet gap (40), which--relativeto the longitudinal extension of said drive shaft--extend substantiallyaxially oriented.
 10. A multi-disc brake according to claim 9characterized in that said passage openings (47) extend obliquelyinclined, forming an acute angle, in a direction toward said inlet gap(40).
 11. A multi-disc brake according to claim 10, characterized inthat the total cross section of said passage openings (47) substantiallycorresponds to the cross section of said inlet gap (40).
 12. Amulti-disc brake according to claim 1, characterized in that said ducts(34), in relation to a longitudinal central plane of said drive shaft,discharge between two adjacent inner brake discs (27) oriented with saidouter discs (38).
 13. A multi-disc brake according to claim 1,characterized in that the friction surfaces of said inner and/or outerbrake discs (27, 28) are provided with groove-like depressions which--asseen in top view on said friction surfaces--extend radially or curved ina manner such that in both directions of rotation of said multi-discbrake (29) a feeding action on the coolant to exerted.
 14. A multi-discbrake within a wheel head whose ring-gear carrier (3) positively mesheswith an external gearing (14) in an internal gearing (16) of a ring gear(15) according to claim 1, characterized in that said internal gearing(14) has longitudinally extending passages (50) for the coolantdistributed on the periphery.
 15. A multi-disc brake according to claim14, characterized in that said passages (50) discharge in a collectorring (49) connected with said drain pipe (51, 52) for the coolant.
 16. Amulti-disc brake according to claim 15 characterized in that saidcollector ring (49) is formed by an end face of said ring gear (15), asurface of said ring-gear carrier (3) and an external ring.
 17. Amulti-disc brake according to claim 1, characterized in that an externalwall (6) of said feed gap (8) is cup-like, enlarged in a directiontoward said disc carrier (10).
 18. A multi-disc brake according to claim1, characterized in that said annular gap (8) exclusively forms the feedpipe (53) of the coolant.
 19. A multi-disc brake according to claim 1,characterized in that at least one feed pipe (54) for the coolantextending parallel with said drive shaft (7) discharges in said annulargap (18).
 20. A multi-disc brake according to claim 1, characterized inthat when said drive shaft (7) is stationary, the coolant dischargesoutwardly via said drain pipe (51, 52) by said passage openings (47) ofsaid disc carrier (10), said inlet gap (40) of said feed gap (41) andsaid annular gap (8).
 21. A multi-disc brake according to claim 1,characterized in that when said drive shaft (7) is stationary, thecoolant discharges via said passage openings (47) of said disc carrier(10), said inlet gap (40) of said feed gap (41) and said annular gap(8).
 22. A multi-disc brake according to claim 20, characterized in thatsaid drain pipe (51, 52) and/or said annular gap (8) is/are connectedwith the interior of the axle body.
 23. A multi-disc brake according toclaim 1, characterized in that said multi-disc brake (29) and aplanetary transmission (13) are together situated in a wheel head (1)within a wheel hub (20).